Bearing constituent member, method of manufacturing bearing constituent member, and rolling bearing

Abstract

A bearing constituent member includes a base material including steel and a carbonitrided layer that is a surface layer on the steel, the steel including 0.3 to 0.45 mass % of carbon, 0.5 mass % or lower of silicon, 0.4 to 1.5 mass % of manganese, 0.3 to 2 mass % of chromium, 0.1 to 0.35 mass % of molybdenum, 0.2 to 0.4 mass % of vanadium, and a remainder of iron and unavoidable impurities. Surface Vickers hardness at a position at a depth of 50 μm from a surface of a rolling sliding surface is 700 to 800, internal hardness is 550 to 690 in terms of Vickers hardness, and an amount of residual austenite in a range from the surface to a depth of 10 μm is at least 30 vol %.

Description

INCORPORATION BY REFERENCE[0001]The disclosure of Japanese Patent Application No. 2015-240441 filed on Dec. 9, 2015 including the specification, drawings and abstract is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a bearing constituent member, a method of manufacturing the bearing constituent member, and a rolling bearing including the bearing constituent member.[0004]2. Description of Related Art[0005]In order to lubricate a rolling bearing, a lubricant is used. A foreign material such as wear debris may be in the lubricant. In a case where a rolling bearing is used under conditions in which a foreign material is in a lubricant, the foreign material is pressed against outer and inner rings or a rolling element, and surfaces of the outer and inner rings or a surface of the rolling element may be damaged. A portion in the surface that is damaged by a foreign material causes fatigue s...

AI Technical Summary

Benefits of technology

[0007]In a medium-sized rolling bearing used in a construction machine or the like, in order to secure the hardenability of steel during manufacturing, chromium-molybdenum steel (SCM steel) or nickel-chrome-molybdenum steel (SNCM steel) is used. However, in the medium-sized rolling bearing, relatively large-sized steel is used, and therefore, in order to secure sufficient internal hardness of the rolling bearing, it is necessary to perform a carburizing treatment or a carbonitriding treatment for a very long time period of 930 minutes as shown in FIG. 20. In addition, in SCM steel and SNCM steel, crystal grains are coarsened due to a long time period of the carburizing treatment or the carbonitriding treatment, and toughness deteriorates. Therefore, in a case where SCM steel or SNCM steel is used as steel, it is necessary to perform secondary quenching for reducing the grain size of the coarsened crystal grains, in addition to a carburizing quenching treatment or a carbonitriding quenching treatment, as shown in FIG. 20. Therefore, in a case where SCM steel or SNCM steel is used, the number of processes is increased during the manufacturing and thus the manufacturing cost is increased.

[0008]The present invention provides a bearing constituent member which can be inexpensively manufactured and in which a long lifetime can be secured under conditions in which a foreign material is in a lubricant, a method of manufacturing the bearing constituent member, and a rolling bearing.

[0010]In the bearing constituent member according to the first aspect of the present invention, the surface Vickers hardness at the position at the depth of 50 μm from a surface of the rolling sliding surface is 700 to 800, the internal hardness is 550 to 690 in terms of Vickers hardness, and the amount of residual austenite in the range from the surface to the depth of 10 μm is at least 30 vol %. Thus, in the bearing constituent member according to the above-described aspect of the present invention, a long lifetime can be secured even under conditions in which a foreign material is in a lubricant. Further, the cost of the steel having the above-described composition is low and the steel having the above-described composition has excellent workability. Therefore, the bearing constituent member according to the above-described aspect of the present invention can be inexpensively manufactured.

[0011]A second aspect of the present invention relates to a rolling bearing including an outer ring that has a raceway surface on an inner periphery thereof; an inner ring that has a raceway surface on an outer periphery thereof; and a plurality of rolling elements disposed between the raceway surface of the outer ring and the raceway surface of the inner ring. At least one of the outer ring, the inner ring, and the plurality of rolling elements is constituted by the above-described bearing constituent member. Since the rolling bearing according to the above-described aspect of the present invention includes the above-described bearing constituent member, the above-described excellent effects can be obtained. The rolling bearing may be a medium-sized tapered roller bearing. In this case, as compared to a medium-sized tapered roller bearing of the related art which is obtained from steel including large amounts of nickel, chromium, and molybdenum, the rolling bearing according to the above-described aspect of the present invention can be inexpensively manufactured within a short time period. Further, even under conditions in which a foreign material is in a lubricant, it is possible to secure a lifetime that is equal to or longer than that of a medium-sized tapered roller bearing of the related art which is obtained from steel including large amounts of nickel, chromium, and molybdenum.

[0013]In the method of manufacturing a bearing constituent member according to the above-aspect of the present invention, the carbonitriding quenching treatment of heating and holding the formed material, which is formed of the steel having the above-described composition, at 830° C. to 930° C. in the carbonitriding atmosphere having the carbon potential of 1 to 1.3 and the ammonia concentration of 1 to 6 vol % and then quenching the formed material is performed, and a tempering treatment of tempering the formed material at 150° C. to 250° C. is performed. Therefore, a bearing constituent member having the above-described excellent effects can be obtained.

[0014]According to the bearing constituent member, the method of manufacturing the bearing constituent member, and the rolling bearing including the bearing constituent member according to the aspects of the invention, the bearing constituent member can be inexpensively manufactured, and a long lifetime can be secured even under conditions in which a foreign material is in a lubricant.

Problems solved by technology

However, in the steel disclosed in JP 4-26752 A, the nickel content, the chromium content, and the molybdenum content are high, which causes an increase in the manufacturing cost of a bearing constituent member.

However, in the medium-sized rolling bearing, relatively large-sized steel is used, and therefore, in order to secure sufficient internal hardness of the rolling bearing, it is necessary to perform a carburizing treatment or a carbonitriding treatment for a very long time period of 930 minutes as shown in FIG. 20.

In addition, in SCM steel and SNCM steel, crystal grains are coarsened due to a long time period of the carburizing treatment or the carbonitriding treatment, and toughness deteriorates.

Therefore, in a case where SCM steel or SNCM steel is used, the number of processes is increased during the manufacturing and thus the manufacturing cost is increased.

Images